Manufacturing techniques and corresponding devices for magnetic tunnel junction devices

ABSTRACT

Some embodiments relate to a magnetoresistive random-access memory (MRAM) cell. The cell includes a bottom electrode having a central bottom electrode portion surrounded by a peripheral bottom electrode portion. Step regions of the conductive bottom electrode couple the central and peripheral bottom electrode portions to one another such that an upper surface of the central portion is recessed relative to an upper surface of the peripheral portion. A magnetic tunneling junction (MTJ) has MTJ outer sidewalls which are disposed over the bottom central electrode portion and which are arranged between the step regions. A top electrode is disposed over an upper surface of the MTJ. Other devices and methods are also disclosed.

REFERENCE TO RELATED APPLICATION

This Application is a Divisional of U.S. application Ser. No. 14/801,988filed on Jul. 17, 2015, the contents of which are hereby incorporated byreference in their entirety.

BACKGROUND

Many modern day electronic devices contain electronic memory. Electronicmemory may be volatile memory or non-volatile memory. Non-volatilememory is able to retain its stored data in the absence of power,whereas volatile memory loses its data memory contents when power islost. Magnetoresistive random-access memory (MRAM) is one promisingcandidate for next generation of non-volatile electronic memory due toadvantages over current electronic memory. Compared to currentnon-volatile memory, such as flash random-access memory, MRAM typicallyis faster and has better endurance. Compared to current volatile memory,such as dynamic random-access memory (DRAM) and static random-accessmemory (SRAM), MRAM typically has similar performance and density, butlower power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of an MRAMcell, including a magnetic tunneling junction (MTJ), according to thepresent disclosure.

FIG. 2 illustrates a cross-sectional view of some embodiments of anintegrated circuit including MRAM cells.

FIG. 3 illustrates a top view of some embodiments of FIG. 2's integratedcircuit including MRAM cells.

FIG. 4 illustrates an enlarged cross-sectional view an MRAM cell of FIG.2's integrated circuit.

FIG. 5 illustrates a flow chart of some embodiments of a method formanufacturing an MRAM cell according to the present disclosure.

FIGS. 6 through 16 illustrate a series of incremental manufacturingsteps as a series of cross-sectional views, according to the method ofFIG. 5.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples,for implementing different features of this disclosure. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

A magnetoresistive random-access memory (MRAM) cell includes upper andlower electrodes, and a magnetic tunnel junction (MTJ) arranged betweenthe upper and lower electrodes. In conventional MRAM cells, the lowerelectrode is coupled to an underlying metal layer (e.g., metal 1, metal2, metal 3, etc.) by a contact or via. Although use of this couplingcontact or via is widely adopted, the overall height of this underlyingcontact or via plus the MRAM cell thereover is large relative to typicalvertical spacing between adjacent metal layers (e.g., between a metal 2layer and a metal 3 layer). To make this height more in line with thevertical spacing between adjacent metal layers, the present disclosurecouples the lower electrodes of MRAM cells directly to an underlyingmetal layer without the use of contacts or vias. Advantageously, byforming the lower electrode of the MRAM cell in direct electricalcontact with the underlying metal layer without a contact or via therebetween (e.g., by “squeezing out” the conventional contact or via), theimproved MRAM cell has a shorter profile and is more compatible withexisting back end of line (BEOL) metallization techniques. Further,whereas traditional MRAM devices have required the use a chemicalmechanical planarization (CMP) operation to planarize an upper surfaceof the bottom electrode, aspects of the present disclosure can avoid theuse of this CMP operation. Avoiding this CMP operation helps tostreamline manufacturing, which can help reduce manufacturing costs,limit various types of defects, and improve yields.

Referring to FIG. 1, a cross-sectional view of an MRAM cell 100 inaccordance with some embodiments is provided. The MRAM cell 100 includesa bottom electrode 102 and a top electrode 104, which are separated fromone another by a magnetic tunnel junction (MTJ) 106. The MTJ 106includes a lower ferromagnetic electrode 108 and an upper ferromagneticelectrode 110, which are separated from one another by a tunnelingbarrier layer 112. In some embodiments, the lower ferromagneticelectrode 108 can have a fixed or “pinned” magnetic orientation, whilethe upper ferromagnetic electrode 110 has a variable or “free” magneticorientation, which can be switched between two or more distinct magneticpolarities that each represents a different data state, such as adifferent binary state. In other implementations, however, the MTJ 106can be vertically “flipped”, such that the lower ferromagnetic electrodehas a “free” magnetic orientation, while the upper ferromagneticelectrode 110 has a “pinned” magnetic orientation.

Notably, rather than a contact or via coupling the bottom electrode 102to an underlying metal layer 116 (underlying metal layer 116 is disposedwithin inter-metal dielectric (IMD) layer 118), the bottom electrode 102itself is in direct electrical contact with the underlying metal layer116. To achieve this coupling, the bottom electrode 102 has a centralbottom electrode portion 120 which extends downwardly through anIMD-protection layer 122 to contact the underlying metal layer 116. Stepregions 124 extend upwardly from the central portion of the bottomelectrode (120) and along the sidewalls of the IMD-protection layer 122to couple the central portion of the bottom electrode (120) toperipheral bottom electrode portions (126), such that an upper surfaceof the central portion (120 a) is recessed relative to an upper surfaceof the peripheral portion (126 a). The central bottom electrode portion120, step regions 124, and peripheral portions 126 can be a continuous,seamless body of material. The upper surface of the central portion (120a) can be substantially and continuously planar between the step regions124, and a lower surface of the MTJ 106 is disposed on the upper surfaceof the central portion 120 a. Sidewall spacers 128 extend continuouslyover upper surfaces of the peripheral portions 126, step region 124, andoptionally outer portions of central bottom electrode portion 120, andextend upwardly along sidewalls of the MTJ 106 and top electrode 104.

Because there is no via or contact between the bottom electrode 102 andunderlying metal layer 116 and because the upper surface of the centralportion (120 a) is recessed, the overall height of the MRAM cell,h_(cell) (as measured from the uppermost surface of the underlying metallayer (116 a) to upper surface of top electrode (104 a)) can be reducedrelative to previous approaches. Compared to previous approaches, thisreduced height, h_(cell), makes the MRAM cell 100 more easily compatiblewith BEOL process flows.

FIG. 2 illustrates a cross sectional view of some embodiments of anintegrated circuit 200, which includes MRAM cells 202 a, 202 b disposedin an interconnect structure 204 of the integrated circuit 200. Theintegrated circuit 200 includes a substrate 206. The substrate 206 maybe, for example, a bulk substrate (e.g., a bulk silicon substrate) or asilicon-on-insulator (SOI) substrate. The illustrated embodiment depictsone or more shallow trench isolation (STI) regions 208, which mayinclude a dielectric-filled trench within the substrate 206.

Two word line transistors 210, 212 are disposed between the STI regions208. The word line transistors 210, 212 include word line gateelectrodes 214, 216, respectively; word line gate dielectrics 218, 220,respectively; word line sidewall spacers 222; and source/drain regions224. The source/drain regions 224 are disposed within the substrate 206between the word line gate electrodes 214, 216 and the STI regions 208,and are doped to have a first conductivity type which is opposite asecond conductivity type of a channel region under the gate dielectrics218, 220, respectively. The word line gate electrodes 214, 216 may be,for example, doped polysilicon or a metal, such as aluminum, copper, orcombinations thereof. The word line gate dielectrics 218, 220 may be,for example, an oxide, such as silicon dioxide, or a high-κ dielectricmaterial. The word line sidewall spacers 222 can be made of SiN, forexample.

The interconnect structure 204 is arranged over the substrate 206 andcouples devices (e.g., transistors 210, 212) to one another. Theinterconnect structure 204 includes a plurality of IMD layers 226, 228,230, and a plurality of metallization layers 232, 234, 236 which arelayered over one another in alternating fashion. The IMD layers 226,228, 230 may be made, for example, of a low κ dielectric, such asun-doped silicate glass, or an oxide, such as silicon dioxide, or anextreme low κ dielectric layer. The metallization layers 232, 234, 236include metal lines 238, 240, 241, 242, which are formed withintrenches, and which may be made of a metal, such as copper or aluminum.Contacts 244 extend from the bottom metallization layer 232 to thesource/drain regions 224 and/or gate electrodes 214, 216; and vias 246,248 extend between the metallization layers 232, 234, 236. The contacts244 and the vias 246, 248 extend through dielectric-protection layers250, 252 (which can be made of dielectric material and can act as etchstop layers during manufacturing). The dielectric-protection layers 250,252 may be made of an extreme low-κ dielectric material, such as SiC,for example. The contacts 244 and the vias 246, 248 may be made of ametal, such as copper or tungsten, for example.

MRAM cells 202 a, 202 b, which are configured to store respective datastates, are arranged within the interconnect structure 204 betweenneighboring metal layers. The MRAM cell 202 a includes a bottomelectrode 254 and a top electrode 256, which are made of conductivematerial. Between its top and bottom electrodes 254, 256, MRAM cell 202a includes an MTJ 258. MRAM cell 202 a also includes MRAM sidewallspacers 260. In some embodiments, a hardmask 263 covers the topelectrode 256, and via 248 extends downwardly through hardmask 263 toohmically contact top electrode 256. More commonly, however, thehardmask 263 and/or via 248 are not present, and for example, the metalline 242 can be co-planar with and in direct electrical contact with(e.g., ohmically coupled to) a top surface of top electrode 256 (seee.g., FIG. 16 further herein).

FIG. 3 depicts some embodiments of a top view of FIG. 2's integratedcircuit 200 as indicated in the cut-away lines shown in FIGS. 2-3. Ascan be seen, the MRAM cells 202 a, 202 b can have a square orrectangular shape in some embodiments. In other embodiments, however,for example due to practicalities of many etch processes, the corners ofthe illustrated square shape can become rounded, resulting in MRAM cells202 a, 202 b having a square or rectangular shape with rounded corners,or having a circular or oval shape. The MRAM cells 202 a, 202 b arearranged over metal lines 240, 241, respectively, and have bottomelectrodes 254 in direct electrical connection with the metal lines 240,241, respectively, without vias or contacts there between.

Referring now to FIG. 4, an enlarged cross-sectional view of FIG. 2'sMRAM cell 202 a is provided. As shown, the MRAM cell 202 a includesbottom electrode 254 and top electrode 256 with MTJ 258 disposed betweenthe bottom electrode 254 and top electrode 256. A central portion of thebottom electrode (261) extends downwardly through in an opening in thedielectric-protection layer 252 to make electrical contact withunderlying metal line 240. The central portion of the bottom electrode(261) has a bottom electrode width, which can be equal to a width of avia. Step regions 262 extend upwardly from the central portion of thebottom electrode, and peripheral regions 264 extend outwardly from thestep regions. The central region has an upper surface 261 a that isrecessed relative to upper surface of peripheral regions 264 a, and theMTJ 258 is disposed on this upper surface 261 a. Sidewall spacers 260are disposed over the peripheral portions of the bottom electrode 264.

In the illustrated embodiment, the MTJ 258 includes a lowerferromagnetic electrode 266 (which can have a pinned magneticorientation) and an upper ferromagnetic electrode 268 (which can have afree magnetic orientation). A tunneling barrier layer 270 is disposedbetween the lower and upper ferromagnetic electrodes 266, 268; and acapping layer 272 is disposed over the upper ferromagnetic electrode268. The lower ferromagnetic electrode 266 can be a syntheticanti-ferromagnetic (SAF) structure that includes a top pinnedferromagnetic layer 274, a bottom pinned ferromagnetic layer 276, and ametal layer 278 sandwiched between the top and bottom pinnedferromagnetic layers 274, 276.

In some embodiments, the upper ferromagnetic electrode 268 comprises Fe,Co, Ni, FeCo, CoNi, CoFeB, FeB, FePt, FePd, or the like, and has athickness ranging between approximately 8 angstroms and approximately 13angstroms. In some embodiments, the capping layer 272 comprises WO₂,NiO, MgO, Al₂O₃, Ta₂O₅, MoO₂, TiO₂, GdO, Al, Mg, Ta, Ru, or the like. Insome embodiments, the tunneling barrier layer 270 provides electricalisolation between the upper ferromagnetic electrode 268 and the lowerferromagnetic electrode 266, while still allowing electrons to tunnelthrough the tunneling barrier layer 270 under proper conditions. Thetunneling barrier layer 270 may comprise, for example, magnesium oxide(MgO), aluminum oxide (e.g., Al₂O₃), NiO, GdO, Ta₂O₅, MoO₂, TiO₂, WO₂,or the like. Further, the tunneling barrier layer 270 may be, forexample, about 0.5-2 nanometers thick.

In operation, the variable magnetic polarity of the upper (e.g., free)ferromagnetic electrode 268 is typically read by measuring theresistance of the MTJ 258. Due to the magnetic tunnel effect, theresistance of the MTJ 258 changes with the variable magnetic polarity.Further, in operation, the variable magnetic polarity is typicallychanged or toggled using the spin-transfer torque (STT) effect.According to the STT effect, current is passed across the MTJ 258 toinduce a flow of electrons from the lower (e.g., pinned) ferromagneticelectrode 266 to the upper (e.g., free) ferromagnetic electrode 268. Aselectrons pass through the lower ferromagnetic electrode 266, the spinsof the electrons are polarized. When the spin-polarized electrons reachthe upper ferromagnetic electrode 268, the spin-polarized electronsapply a torque to the variable magnetic polarity and toggle the state ofthe upper ferromagnetic electrode 268. Alternative approaches to readingor changing the variable magnetic polarity are also amenable. Forexample, in some alternate approaches magnetization polarities of thepinned and/or free ferromagnetic electrodes 266/268 are perpendicular toan interface between the tunneling barrier layer 270 and the pinnedand/or free ferromagnetic electrode 266/268, making the MTJ 258 aperpendicular MTJ.

Advantageously, because the bottom electrode 254 itself is in directelectrical contact with the underlying metal line 240, the overallheight of the MRAM cells 202 a, 202 b can be reduced relative toprevious approaches. Compared to previous approaches, this reducedheight makes the MRAM cells 202 a, 202 b more easily compatible withBEOL process flows. Thus, formation of MRAM cells 202 a, 202 b providesbetter MRAM operations with reduced manufacturing cost.

With reference to FIG. 5, a flowchart illustrates some embodiments of amethod 500 for manufacturing a semiconductor structure having a MRAMcell according to some embodiments of the present disclosure. It will beappreciated that the illustrated method is not interpreted in a limitingsense, and that alternate methods for forming a MRAM cell may also beconsidered within the scope of the disclosure.

At 502, a semiconductor substrate with an interconnect structuredisposed thereon is provided. The interconnect structure includes adielectric layer and a metal line extending horizontally through thedielectric layer.

At 504, a dielectric-protection layer, which can be made of dielectricmaterial and can act as etch stop, is formed over an upper surface ofthe dielectric layer. The dielectric-protection layer exhibits anopening that leaves at least a portion of an upper surface of the metalline exposed.

At 506, a conformal bottom electrode layer is formed over thedielectric-protection layer. The conformal bottom electrode layerextends downwardly into the opening to make direct electrical contactwith the metal line.

At 508, a magnetic tunnel junction (MTJ) stack is formed over theconformal bottom electrode layer. The MTJ stack can include upper andlower ferromagnetic layers, which are spaced apart by a tunnelingbarrier layer. One of the lower and upper ferromagnetic layers is apinned layer with a fixed ferromagnetic polarity, while the other of thelower and upper ferromagnetic layers is a free layer with a variableferromagnetic polarity.

At 510, a top electrode layer is formed over the magnetic tunneljunction stack.

At 512, a mask layer is formed and patterned over the top electrodelayer. The patterned mask has outer sidewalls which are disposed over acentral portion of the bottom electrode.

At 514, an etch is carried out with the patterned mask in place toexpose an upper surface of a peripheral portion of the bottom electrodelayer while a patterned top electrode and MTJ stack remain over thecentral portion of the bottom electrode.

At 516, sidewall spacers are formed over the exposed upper surface ofthe peripheral portion.

At 518, an inter-metal dielectric (IMD) layer is formed over thesidewall spacers.

At 520, the IMD layer is etched back, and an upper metal layer is formedover the top electrode. The upper metal layer, as formed, is inelectrical contact with top electrode.

Advantageously, the method 500 includes a reduced number of processingsteps as it does not require the use of a CMP operation on the bottomelectrode. The above described method also helps in having a reducedthickness for the overall MRAM cell, which promotes a simple and costeffective structure.

While the disclosed methods (e.g., the method described by the flowchart500, methods depicted in FIGS. 6-16, and un-illustrated methods) may beillustrated and/or described herein as a series of acts or events, itwill be appreciated that the illustrated ordering of such acts or eventsare not to be interpreted in a limiting sense. For example, some actsmay occur in different orders and/or concurrently with other acts orevents apart from those illustrated and/or described herein. Further,not all illustrated acts may be required to implement one or moreaspects or embodiments of the description herein, and one or more of theacts depicted herein may be carried out in one or more separate actsand/or phases.

With reference to FIGS. 6 through 16, cross-sectional views of someembodiments of a semiconductor structure having an MRAM cell at variousstages of manufacture are provided to illustrate an example consistentwith the method of FIG. 5. Although FIGS. 6 through 16 are described inrelation to FIG. 5's method, it will be appreciated that the structuresdisclosed in FIGS. 6 through 16 are not limited to the method, butinstead may stand alone as structures independent of the method.Similarly, although the FIG. 5′a method is described in relation toFIGS. 6 through 16, it will be appreciated that FIG. 5's method is notlimited to the structures disclosed in FIGS. 6 through 16, but insteadmay stand alone independent of the structures disclosed in FIGS. 6through 16 and/or may use other structures.

FIG. 6 illustrates a cross-sectional view 600 of some embodimentscorresponding to Act 502 of FIG. 5.

In FIG. 6, a substrate 206 with an interconnect structure 204 disposedthere over is provided. The interconnect structure 204 includes an IMDlayer 228 and a metal line 240 which extends horizontally through theIMD layer 228. The IMD layer 228 can be an oxide, such as silicondioxide, a low-κ dielectric material, or an extreme low-κ dielectricmaterial. The metal line 240 can be made of a metal, such as aluminum,copper, or combinations thereof. In some embodiments, the substrate 206can be a bulk silicon substrate or a semiconductor-on-insulator (SOI)substrate (e.g., silicon on insulator substrate). The substrate 206 canalso be a binary semiconductor substrate (e.g., GaAs), a tertiarysemiconductor substrate (e.g., AlGaAs), or a higher order semiconductorsubstrate, for example. In many instances, the substrate 206 manifestsas a semiconductor wafer during the method 500, and can have a diameterof 1-inch (25 mm); 2-inch (51 mm); 3-inch (76 mm); 4-inch (100 mm);5-inch (130 mm) or 125 mm (4.9 inch); 150 mm (5.9 inch, usually referredto as “6 inch”); 200 mm (7.9 inch, usually referred to as “8 inch”); 300mm (11.8 inch, usually referred to as “12 inch”); 450 mm (17.7 inch,usually referred to as “18 inch”); for example. After processing iscompleted, for example after MRAM cells are formed, such a wafer canoptionally be stacked with other wafers or die, and is then singulatedinto individual die which correspond to individual ICs.

FIG. 7 illustrates a cross-sectional view 700 of some embodimentscorresponding to Act 504 of FIG. 5.

In FIG. 7, a dielectric-protection layer is formed over IMD layer 228and over metal line 240. After the dielectric-protection layer isformed, a first mask 702, such as a photoresist mask, is then formedover the dielectric-protection layer. A first etch 704 is then carriedout with the first mask 702 in place to form patterneddielectric-protection layer 252. The dielectric-protection layer 252 ismade of dielectric material, such as an oxide or ELK dielectric, andacts as an etch-stop layer. In some embodiments, thedielectric-protection layer 252 comprises SiC having a thickness ofapproximately 200 Angstroms. The first etch can be performed when a wetetchant or a plasma etchant is applied to the dielectric-protectionlayer 252 with the first mask 702 in place, and forms an opening 706.The opening 706 can have a width, w, which corresponds to a width of avia (e.g., via 246, FIG. 2) in the interconnect structure 204. The firstmask 702 can be removed after the etching.

FIG. 8 illustrates a cross-sectional view 800 of some embodimentscorresponding to Act 506 of FIG. 5.

In FIG. 8, a bottom electrode layer 254′ is formed over thedielectric-protection layer 252, and extends downwardly into the opening706 to make direct electrical contact with the metal line 240. Thebottom electrode layer 254′ is a conformal layer that may be acontinuous conductive body. The bottom electrode layer 254′ may be aconductive material, such as, for example, titanium nitride, tantalumnitride, titanium, tantalum, or a combination of one or more of theforegoing. Further, the bottom electrode layer 254′ may be, for example,about 10-100 nanometers thick in some embodiments.

FIG. 9 illustrates a cross-sectional view 900 of some embodimentscorresponding to Acts 508, 510, and 512 of FIG. 5.

In FIG. 9, a magnetic tunneling junction (MTJ) stack 258′ is formed overan upper surface of the bottom electrode layer 254′, a capping layer272′ is formed over MTJ stack 258′, and a top electrode layer 256′ isformed over the capping layer 272′. The MTJ stack 258′ comprises a lowerferromagnetic layer 266′, a tunneling barrier layer 270′, and an upperferromagnetic layer 268′. In some embodiments, the lower ferromagneticlayer 266′ has a fixed magnetic polarity, and includes lower and upperferromagnetic electrode layers 276′, 274′, respectively, with a metallayer 278′ disposed there between. In these embodiments, the upperferromagnetic layer 268′ can be configured to switch between at leasttwo magnetic polarities. In some embodiments, the lower ferromagneticlayer 266′ comprises FePt or CoFeB having a thickness ranging betweenapproximately 8 angstroms and approximately 13 angstroms, and the upperferromagnetic layer 268′ comprises single or multiple layers of Co, Nior Ru. The top electrode layer 256′ may be a conductive material, suchas, for example, titanium nitride, tantalum nitride, titanium, tantalum,or a combination of one or more of the foregoing. Further, the topelectrode layer 256′ may be, for example, about 10-100 nanometers thick.A mask 902 is disposed over an upper surface of the top electrode layer256′. In some embodiments, the mask 902 is a photoresist mask, but canalso be a hard mask such as a nitride mark.

FIGS. 10-11 illustrate cross-sectional views 1000, 1100 of someembodiments corresponding to Act 514 of FIG. 5.

As illustrated by FIG. 10, with the mask 902 in place, a second etch1002 is performed. The second etch 1002 proceeds through regions of topelectrode layer 256′, capping layer 272′, and MTJ stack 258′ which arenot covered by mask 902. In some embodiments, the second etch 1002comprises, applying a wet etchant or a plasma etchant for apredetermined period of time, and results in the structure of FIG. 11.Thus, the second etch 1002 removes portions of the MTJ stack not coveredby the mask 902 and stops on the bottom electrode layer 254′.

FIGS. 12-13 illustrate cross-sectional views 1200, 1300 of someembodiments corresponding to Act 516 of FIG. 5.

As illustrated in FIG. 12, a sidewall spacer layer 260′ is formed overthe structure, lining the upper surface and sidewalls of the cappinglayer 272, top electrode 256, and MTJ 258. In some embodiments, thesidewall spacer layer 260′ may be formed by any suitable depositiontechnique and is typically formed conformally. Further, the sidewallspacer layer 260′ may be formed of, for example, silicon nitride,silicon carbide, or a combination of one or more of the foregoing. Evenmore, the sidewall spacer layer 260′ may be formed with a thickness of,for example, about 500 Angstroms.

In FIG. 13, a third etch 1302 is performed into the sidewall spacerlayer 260′ to etch sidewall spacer layer 260′ back to remove lateralstretches of the sidewall spacer layer 260′, thereby forming sidewallspacers 260. The third etch 1302 also removes lateral stretches of thebottom electrode layer 254′ to form a bottom electrode 254. In someembodiments, the process for performing the third etch 1302 includesexposing the sidewall spacer layer 260′ to an etchant for apredetermined period of time sufficient to etch through the thickness ofthe sidewall spacer layer 260′ and the bottom electrode layer 254′. Theetchant is typically preferential of the sidewall spacer layer 260′ andthe bottom electrode layer 254′, relative to the dielectric-protectionlayer 252. In some embodiments, the upper outer corners of sidewallspacers 260 may be more or less squared-off or rounded, compared to theillustration of FIG. 13.

FIGS. 14-15 illustrates cross-sectional views 1400, 1500 of someembodiments corresponding to Act 518 of FIG. 5.

As illustrated in FIG. 14, an IMD layer 230′ is formed over thestructure. In some embodiments, IMD layer 230′ may be formed by anysuitable deposition technique and is typically formed conformally.Further, the IMD layer 230′ may be formed of, for example a low-κdielectric layer or an ELK dielectric layer, to a thickness ofapproximately 2650 Angstroms. If an ELK dielectric layer is used, acuring process is typically followed after depositing the ELK dielectriclayer to increase its porosity, lower its k value, and improve itsmechanical strengths.

In FIG. 15, the IMD layer 230 has been etched back to substantiallyplanarize an upper surface of the IMD layer 230. In some embodiments,this etch back is achieved by wet or dry etching rather than chemicalmechanical planarization (CMP). Further, in some embodiments, this etchback may be divided into one etch used to planarize the IMD over theMRAM regions and another etch to planarize the IMD over logic regions onthe wafer or IC.

FIG. 16 illustrates cross-sectional view 1600 of some embodimentscorresponding to Act 520 of FIG. 5.

In FIG. 16, an upper metallization layer 236 is formed over the planartop surface of the top electrode 256. The upper metallization layer 236can be a metal line or via and can abut an entire surface area of thetop electrode 256, thereby providing an electrical connection (e.g.,ohmic connection) to the MRAM cell 202 a. In some embodiments, the uppermetallization layer 236 comprises copper, aluminum, tungsten, orcombinations thereof.

It will be appreciated that in this written description, as well as inthe claims below, the terms “first”, “second”, “second”, “third” etc.are merely generic identifiers used for ease of description todistinguish between different elements of a figure or a series offigures. In and of themselves, these terms do not imply any temporalordering or structural proximity for these elements, and are notintended to be descriptive of corresponding elements in differentillustrated embodiments and/or un-illustrated embodiments. For example,“a first dielectric layer” described in connection with a first figuremay not necessarily correspond to a “first dielectric layer” describedin connection with another figure, and may not necessarily correspond toa “first dielectric layer” in an un-illustrated embodiment.

Thus, as can be appreciated from above, some embodiments relate to amagnetoresistive random-access memory (MRAM) cell. The cell includes abottom electrode having a central bottom electrode portion surrounded bya peripheral bottom electrode portion. Step regions of the conductivebottom electrode couple the central and peripheral bottom electrodeportions to one another such that an upper surface of the centralportion is recessed relative to an upper surface of the peripheralportion. A magnetic tunneling junction (MTJ) has MTJ outer sidewallswhich are disposed over the bottom central electrode portion and whichare arranged between the step regions. A top electrode is disposed overan upper surface of the MTJ. Other devices and methods are alsodisclosed.

Other embodiments relate to a method for manufacturing amagnetoresistive random access memory (MRAM) cell. the method including:forming a dielectric layer over a semiconductor substrate; forming anopening in the dielectric layer, and filling the opening with a metallayer; forming an etch stop layer disposed over the upper surface of thedielectric layer, wherein the etch stop layer exhibits an opening thatleaves at least a portion of the upper surface of the metal line or viaexposed; forming a conformal bottom electrode layer over the etch stoplayer and the metal layer, wherein the conductive bottom electrode layerincludes a peripheral portion overlying the etch stop layer and acentral portion extending downward through the opening to the uppersurface of the metal line or via; and forming a magnetic tunnel junctionover the central portion of the conformal conductive bottom electrodelayer.

Still other embodiments relate to an integrated circuit. The integratedcircuit includes a semiconductor substrate and an interconnect structuredisposed over the semiconductor substrate. The interconnect structureincludes a plurality of dielectric layers and a plurality of metallayers stacked over one another in alternating fashion. A metal layerincludes a metal line having an upper surface which is at leastsubstantially planar with an upper surface of a dielectric layeradjacent to the metal line. A dielectric-protection layer is disposedover the upper surface of the dielectric layer and exhibits an openingover at least a portion of the upper surface of the metal line. Aconductive bottom electrode extends downwardly through the opening inthe dielectric protection layer to come into direct electrical contactwith the metal line.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An integrated circuit including a magnetoresistive random access memory (MRAM) cell, comprising: a semiconductor substrate; a via disposed over the semiconductor substrate; a metal line disposed over the via; an etch stop layer partially covering an upper surface of the metal line; a bottom electrode over the etch stop layer, wherein the bottom electrode includes a peripheral portion overlying the etch stop layer and a central portion extending downward through an opening in the etch stop layer to contact the upper surface of the metal line, wherein the central portion of the bottom electrode has a width that is equal to a width of the via; a magnetic tunnel junction (MTJ) over the central portion of the bottom electrode; a top electrode over the MTJ; an inter-metal dielectric (IMD) layer over the etch stop layer and the bottom electrode; and sidewall spacers, separating the MTJ from the IMD layer, which extend over an upper surface of the peripheral portion of the bottom electrode, along sidewalls of the MTJ, and along sidewalls of the top electrode, wherein the sidewalls of the MTJ are in direct contact with inner sidewalls of the sidewall spacers, wherein the sidewall spacers have an outer sidewall which is a continuous arc from the upper surface of the peripheral portion of the bottom electrode to a top surface of the top electrode.
 2. The integrated circuit of claim 1, wherein the bottom electrode is made of titanium nitride, tantalum nitride, titanium, tantalum, or combinations thereof.
 3. The integrated circuit according to claim 1, wherein the magnetic tunnel junction comprises: a lower ferromagnetic electrode disposed over the central portion of the bottom electrode; a tunneling barrier layer disposed over the lower ferromagnetic electrode; an upper ferromagnetic electrode disposed over the tunneling barrier layer; and wherein one of the lower and upper ferromagnetic electrodes has a fixed magnetic orientation while the other of the lower and upper ferromagnetic electrodes has a variable magnetic orientation.
 4. The integrated circuit of claim 1, wherein a step portion of the bottom electrode couples the central and peripheral portions of the bottom electrode to one another such that an upper surface of the central portion is recessed relative to an upper surface of the peripheral portion, and wherein the metal line is in direct electrical contact with the bottom electrode without a via or contact coupling the metal line to the bottom electrode.
 5. The integrated circuit of claim 4, wherein the central portion, the step portion, and the peripheral portion are a continuous seamless body.
 6. The integrated circuit of claim 4, wherein the central portion of the bottom electrode is substantially and continuously planar within an innermost perimeter of the step portion.
 7. The integrated circuit of claim 4, wherein the step portion of the bottom electrode extends downwardly along inner sidewalls of the etch stop layer to adjoin the central portion of the bottom electrode.
 8. The integrated circuit of claim 7, wherein the etch stop layer does not extend directly under the central portion of the bottom electrode.
 9. The integrated circuit of claim 8: wherein the metal line extends horizontally through a dielectric layer, and wherein the etch stop layer extends over the dielectric layer.
 10. An integrated circuit including a magnetoresistive random access memory (MRAM) cell arranged in an interconnect structure over a semiconductor substrate, wherein the interconnect structure includes a metal line arranged over a via and an inter-metal dielectric (IMD) layer surrounding the metal line and the via, comprising: a dielectric protection layer over an upper surface of the metal line; a bottom electrode including a peripheral portion overlying the dielectric protection layer and a central portion extending through an opening in the dielectric protection layer to contact the upper surface of the metal line, wherein the central portion of the bottom electrode has a width that is equal to a width of the via; a magnetic tunnel junction over the central portion of the bottom electrode; a top electrode over the magnetic tunnel junction; and sidewall spacers arranged over an upper surface of the peripheral portion of the bottom electrode and separating the IMD layer from the magnetic tunnel junction, wherein the sidewall spacers have outer sidewalls which are substantially planar from the upper surface of the peripheral portion of the bottom electrode to a top surface of the sidewall spacers or which monotonically increase in height from the upper surface of the peripheral portion of the bottom electrode to a top surface of the top electrode, wherein sidewalls of the magnetic tunnel junction and sidewalls of the top electrode are in direct contact with the sidewall spacers.
 11. The integrated circuit of claim 10, wherein a step portion of the bottom electrode couples the central and peripheral portions of the bottom electrode to one another such that an upper surface of the central portion is recessed relative to the upper surface of the peripheral portion.
 12. The integrated circuit of claim 11, wherein the step portion of the bottom electrode extends downwardly along inner sidewalls of the dielectric protection layer to adjoin the central portion of the bottom electrode.
 13. The integrated circuit of claim 12, wherein the dielectric protection layer does not extend directly under the central portion of the bottom electrode.
 14. The integrated circuit of claim 12: wherein the metal line extends horizontally through a dielectric layer, and wherein the dielectric protection layer extends over the dielectric layer.
 15. The integrated circuit of claim 11, wherein the central portion, the step portion, and the peripheral portion are a continuous seamless body.
 16. An integrated circuit including a magnetoresistive random access memory (MRAM) cell arranged in an interconnect structure over a semiconductor substrate, wherein the interconnect structure includes a metal line arranged over a via, comprising: an etch stop layer over an upper surface of the metal line; a bottom electrode including a peripheral portion overlying the etch stop layer and a central portion extending through an opening in the etch stop layer to contact the upper surface of the metal line, wherein the central portion of the bottom electrode has a width that is equal to a width of the via; a magnetic tunnel junction over the central portion of the bottom electrode, the magnetic tunnel junction having a lower surface at a height that is below a height of the upper surface of the peripheral portion of the bottom electrode; a top electrode over the magnetic tunnel junction; sidewall spacers arranged over an upper surface of the peripheral portion of the bottom electrode, wherein the sidewall spacers have outer sidewalls which are substantially planar from the upper surface of the peripheral portion of the bottom electrode to a top surface of the sidewall spacers or which are a continuous arc from the upper surface of the peripheral portion of the bottom electrode to a top surface of the top electrode, wherein a top of the bottom electrode is in direct contact with a bottom surface of the sidewall spacers; and an inter-metal dielectric layer, adjacent to the sidewall spacers, covering the bottom electrode, the sidewall spacers, and the etch stop layer.
 17. The integrated circuit of claim 16, wherein a step portion of the bottom electrode couples the central and peripheral portions of the bottom electrode to one another such that an upper surface of the central portion is recessed relative to an upper surface of the peripheral portion.
 18. The integrated circuit of claim 17, wherein the central portion, step portion, and peripheral portion are a continuous seamless body.
 19. The integrated circuit of claim 18, wherein the central portion of the bottom electrode is substantially and continuously planar within an innermost perimeter of the step portion.
 20. The integrated circuit of claim 19, wherein the bottom electrode is made of titanium nitride, tantalum nitride, titanium, tantalum, or combinations thereof. 